1. Field of Invention
The present invention pertains to a method and apparatus for cleaning tanks and other containers including, but not necessarily limited to, storage tanks used in connection with oil and/or gas operations. More particularly, the present invention pertains to a method and apparatus for cleaning the interior surfaces of tanks, refinery vessels, production vessels, containers and other enclosures, especially in applications where limited space is available.
2. Description of Related Art
Tanks, containers and other similar enclosures are commonly used to store liquids and other fluids in many different industrial, oil and gas, and other applications. Tanks and production vessels of varying sizes and shapes are frequently used to produce and store fluids in connection with the oil and gas industry. By way of example, crude oil produced from wells is typically piped from such wells through production facilities into one or more storage tanks located in general proximity to such wells. Such collected crude oil is thereafter often transported to larger storage tanks at oil refineries or other facilities prior to processing.
When crude oil is stored in a storage tank or production vessel for any length of time, solids and heavier liquid components in such crude oil tend to settle to the bottom of such storage tank or production vessel in the form of sludge. Sludge build up at the bottom of a storage tank or production vessel is undesirable for a number of reasons, the most apparent of which is reduction of the storage capacity of the tank or production vessel.
Additionally, other fluids used in connection with oil and gas operations are also stored in storage tanks. One such fluid that is commonly stored in tanks is drilling mud. Such drilling mud frequently contains chemicals and/or other additives designed to adjust or control certain characteristics of said mud including, without limitation, gelling agents (e.g., colloidal solids and/or emulsified liquids), weighting materials (e.g., barite and/or bentonite, etc.), and/or other chemicals which are used to maintain fluid properties within desired parameters. Further, although drilling fluids have historically been water-based, oil-based and synthetic drilling fluids are commonly used, especially in severe drilling environments. Many drilling mud additives, as well as oil based and synthetic based drilling fluids, can be harmful to personnel and the environment. When drilling muds or other fluids are stored in tanks, solids often fall out of suspension, forming hardened layers at or near the bottom of such tanks. Cleaning of such tanks can be especially challenging when a layer of solids is present. Such solids cannot be simply drained from the tanks/containers; such deposited solids must typically be removed before interior surfaces of the enclosures can be cleaned.
In many cases, personnel are frequently required to physically climb inside storage tanks or production vessel in order to perform manual cleaning operations. Such personnel typically use water hoses, brushes and the like to clean the internal surfaces of such tanks and/or other containers. When sludge or hardened solids are present, such personnel are also often required to manually remove the sludge or deposits from the tanks using shovels or other similar means.
Manual cleaning of storage tanks or production vessels can be very physically demanding on personnel, especially when temperatures inside such tanks are elevated. Moreover, ventilation within such tanks and/or other containers can be very poor, and personnel inside such tanks/containers are frequently exposed to toxins and/or contaminants (typically from solids and/or fluid residue present in such tanks). As a result, manual cleaning of tanks raises safety concerns for personnel performing such cleaning operations.
Regardless of the cleaning methods used, virtually all prior art means of cleaning tanks, or production vessel and/or other containers utilize wash water or some other fluid(s). Such water or other fluid is used to wash sludge, drilling fluid residue, solids and/or other debris from the inner surfaces of such enclosures. After being sprayed, the effluent wash water or other fluid typically contains significant amounts of solids or other contaminants. As a result, such effluent fluid frequently cannot be dumped or otherwise disposed of where the tank, or production vessel or other container is located due to applicable laws, rules or other regulations.
In most cases, in order to avoid environmental contamination and comply with applicable governmental mandates, such effluent fluid and accompanying solids frequently must be collected and transported to another location for off-site disposal. In order to accomplish such off-site disposal, the used wash fluid (and any accompanying solids) typically must be loaded into boxes or other storage containers for transportation away from a tank location. In most cases, large numbers of storage boxes or other portable containers must be rented or purchased in order to hold and transport such waste to off-site disposal facilities, thereby increasing overall project costs. Such storage boxes or other portable containers also take up significant space, which is at a premium on most production facilities, refineries, rigs and other similar facilities (particularly those located in a marine environment).
By separating liquids from solids in the used waste fluid, such liquids can be reclaimed, while separated (substantially “dry”) solids can be loaded into storage boxes or other portable containers for transportation and eventual disposal. Because separated solids take up less volume than a mixture of fluids and solids, separation has the effect of reducing the overall number of storage boxes or containers required to store and transport the waste to an off-site disposal facility. Such separation thereby reduces costs and space requirements associated with such storage boxes and the disposal process.
Additionally, separated liquids often contain water and other non-aqueous liquids including, without limitation, oil or other hydrocarbons. It is frequently beneficial to further separate such liquids to remove any such oil or other hydrocarbons. In many cases, such separated oil or other hydrocarbons can have value and can be re-used or sold for a profit.
Accordingly, there is a need for an efficient and effective means for cleaning tanks, or production vessel and/or similar containers, including oil storage tanks containing crude oil sludge, solids-laden fluids and/or hardened solid deposits that have dropped from suspension. The cleaning system should minimize the need for personnel to physically enter such tanks or other containers, and should permit separation of solids from liquids to permit efficient and economical disposal of such solids. Additionally, the cleaning system should be beneficially compact, and should further permit separation of oil and/or other hydrocarbons from wash liquids.